1. Field of the Invention
The present invention relates to a technique capable of expressing, by using computer graphics (CG) technology, a physical object in which internal scattering of light is caused.
2. Description of the Related Art
Nowadays, using computer graphics (hereinafter, also called “CG”) enables images of physical objects such as metal, glass, and so on to be expressed at a level comparable to the original images. On the other hand, it is difficult for images of the physical objects such as skin, marble, milk, and the like, in which internal scattering of light is caused, to be expressed at a level equivalent to the original images.
In particular, the skin has fine unevenness on its surface, and therefore, it is difficult to express the image thereof in CG at a level comparable to the original image. In order to express the skin image comparable to the original image, it is important to reproduce internal scattering of light entering the skin, as well as to reproduce fine unevenness of the skin such as wrinkles, and pores.
As a method of reproducing the internal scattering, a technique discussed in Japanese Unexamined Patent Application (Translation of PCT Application) No. 2006-506742 is known. In the technique discussed in Japanese Unexamined Patent Application (Translation of PCT Application) No. 2006-506742, a plurality of points is sampled, and blurring processing is performed by integrating pixel values using Bidirectional Scattering Surface Reflectance Distribution Function (BSSRDF function). Meanwhile, as a method for reproducing fine unevenness, processing for expressing the surface shape using a bump mapping method is generally known. Normally, when the skin image is reproduced in CG, the blurring processing is performed after reproducing the fine unevenness thereof.
However, when the blurring processing is performed after reproducing the fine unevenness of the skin surface, there may be a case where the fine unevenness thereof is lost due to the blurring processing. The reason for this is that the blurring processing has been performed without considering height differences on the surface of the skin with fine unevenness.